It is known that flagellin proteins originated from pathogenic bacteria have immune adjuvant effects. The flagellin protein binds to Toll-like receptors (TLRs) 5, activating the NF-κB pathway and then triggering innate immunity and further inducing specific immunity. The mixture or fusion of flagellin protein with a target antigen can significantly enhance the immune responses to the target antigen upon immunization, and can achieve the effects of resisting pathogenic microorganisms carrying the target antigen. But because the flagellin protein originates from pathogenic bacteria, it may have potential risk, and it also can cause inflammatory response, induce a large amount of immune response against itself, lead to possible tolerance and other possible immunological side effects.